The rate of cholesterol influx and the rate of collagen synthesis will be studied in rabbits fed an intermittent cholesterol diet for varying periods of time up to 10 months. Studies will be conducted in vivo to determine the changes in tissue cholesterol, cholesterol esters, phospholipids, and collagen which occur during the 10 month experimental period. Collagen accumulation will be estimated by measuring hydroxyproline levels and collagen synthesis by measuring prolyl hydroxylase activity. Histological studies will also be conducted and correlated to the observed biochemical parameters. In vitro estimation of the rate of cholesterol influx and the rate of collagen synthesis will also be studied in rabbits with different stages of atherosclerosis. In these studies the rate of collagen synthesis will be estimated by measuring C14-proline incorporation and conversion to C14-hydroxyproline. The degree of correlation between collagen synthetic rate of cholesterol influx will be established. The hypothesis to be tested is that the rate of cholesterol influx is affected by changes in connective tissue metabolism.